1. Field of the Invention
The present invention relates generally to selective calling radio display pagers, and more particularly to a radio display pager for a paging system where repeat call transmissions are provided as a system option and all messages are identified with a serial message number.
2. Description of the Related Art
In radio display paging systems, it is the usual practice to send a calling signal by multiplexing messages and the address codes of the message destinations in a frame format. Because of the inability of the paging receiver to acknowledge receipt of a message, a paging system such as the European Radio Message System provides repeat call transmissions as a system option to ensure against possible transmission errors. To enable receivers to identify individual messages, a serial number is attached to all messages. However, due to transmission errors, some of the transmitted calls are disrupted and the messages contained in the calls fail to reach the destination users. If a non-repeat call is lost, an unfavorable situation can occur if the message contained in the lost call is important to the parties concerned. It is therefore desirable to identify the lost call and allow the destination user to communicate the lost message number to the system center to obtain the lost message.
However, due to the presence of repeat calls where the same message number and message are retransmitted, a loss of a single repeat call must be precisely discriminated against a loss of a non-repeat call.